project: reuse loaded refs when resolving HEAD

When the regular checkout has already loaded GitRefs, derive its current
branch and HEAD object from that snapshot instead of spawning
symbolic-ref or rev-parse again. Keep linked Git worktrees on their
worktree-specific HEAD path because the shared repository HEAD is not
authoritative for them.

Bug: 543851900
Bug: 553599402
Change-Id: Iec456be5f3c279865b4165a75d1c6df36e331dbc
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/623181
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/test_git_refs.py b/tests/test_git_refs.py
index 183ed9d74..ab7bdbe97 100644
--- a/tests/test_git_refs.py
+++ b/tests/test_git_refs.py
@@ -59,6 +59,7 @@ def test_reads_refs(tmp_path, reftable):
     branch = _run(repo, "symbolic-ref", "--short", "HEAD")
     head = _run(repo, "rev-parse", "HEAD")
     assert refs.symref("HEAD") == f"refs/heads/{branch}"
+    assert refs.head == f"refs/heads/{branch}"
     assert refs.get("HEAD") == head
     assert refs.get(f"refs/heads/{branch}") == head